The present invention relates to a burner and/or injector panel apparatus, methods of installation and use of the same in a metal-melting furnace, and metal-melting furnace including the same. More particularly, the present invention relates to a sump burner and/or injector panel apparatus, methods of use and installation of the same in a sump area of an electric arc furnace, and an electric arc furnace including the same.
One type of metallurgical process, steelmaking, is very well developed. In general, an electric arc furnace (EAF) is used to make steel by application of an electric arc to melt one or more of scrap metal and/or other alternative iron bearing feed stocks and alloys that are placed within the furnace. One type of EAF has hemispherical lower bowl made of metal. The bottom and sides of the lower bowl are lined with a refractory material forming the hearth. Extending vertically from the bowl are water-cooled sidewalls. Extending between the sidewalls over a molten bath of metal (contained by hearth) is a roof. Electrodes extend through the roof and into the bath. EAFs of the eccentric bottom tapping (EBT) type also include a sump area which is lined with refractory material. The sump area serves the function of containing the molten steel as it is poured from the EAF through a tapping hole.
Generally speaking, scrap metal, or charges, are dumped into the EAF through an opening. Typically these charges further include carbon particulate and other slag forming materials. Other known processes comprise using a ladle for hot or heated metal from a blast furnace and inserting it into the EAF furnace, such as by injection of the DRI by a lance.
There are numerous phases of charge processing in an EAF furnace and/or an EAF-like furnace.
In the melting phase, the electric arc and burners melt the charge burden into a molten pool of metal (melted metal), called an iron carbon melt, which accumulates at the bottom or hearth of the furnace. Thermal energy beyond that supplied by the arc may be provided by burners radially distributed around the furnace. Slag formers such as calcium oxide or magnesium oxide are sometimes injected into the molten pool with one or more injectors.
Most commonly, after melting the charge, an electric arc furnace proceeds to a refining and/or decarburization phase. In this phase, the metal melt continues to be heated by the arc until slag forming materials combine with impurities in the iron carbon melt and rise to the surface as slag. When the iron carbon melt reaches a critical temperature which allows a carbon boil, the charged carbon in the melt combines with any oxygen present in the bath to form carbon monoxide bubbles which rise to the surface of the bath, forming foaming slag. The foaming slag acts as an insulator throughout the furnace.
Further heating and processing is realized by a decarburization process wherein, in typical embodiments of the prior art utilizing advanced or more modern EAF techniques, a high velocity, usually supersonic, flow(s) of oxygen is blown into the metal bath with either lances or burner/lances to decarburize the bath by oxidation of the carbon contained in the bath, forming CO and/or CO2 when combined with the available or excess carbon in the bath. The burner(s)/lance(s) act to more uniformly melt the charge and lessen, or prevent, overheating and minimize the time required for the melt and time that the arc is created.
By injecting the metal bath or liquid metal with oxygen, the dissolved carbon content of the bath can be reduced to a selected or reduced level. It is commonly regarded that if an iron carbon melt is under 2% carbon, the melt becomes steel. EAF steel making processes typically begin with burdens having less than 1% carbon. The carbon in the steel bath is continually reduced until it reaches the content desired for producing a specific grade of steel, such as, for example, and not by way of limitation, down to less than 0.1% for low carbon steels.
Additional chemical energy in the form of carbon or coke particles may also be injected by an injector. Alternatively, a single apparatus (burner/injector) may be used to provide the flame and inject particulate carbon/coke or other slagging materials. Typically, the carbon or coke flow is injected with the aid of a fluidizing gas flow of compressed air, natural gas, nitrogen, and/or the like.
Collectively, burners, lances, injectors, burner/lances, and burner/injectors may be referred to as burners and/or injectors.
One of the problems associated with EAFs is the existence of cold spots. The charged scrap or charge rapidly melts at hot spots located at regions of highest electric current density, but often remains un-melted at cold spots located at regions of lowest electric current density). This creates harsh conditions for the portion of the furnace wall and refractory lining located at the hot spots due to excessive exposure to heat from the arc during the latter portions of the melt down cycle. Scrap located in the cold spot regions receives heat from the arc at a reduced rate during the melt down cycle, thereby creating the cold spots. To melt charge scrap in the cold spots, flames from burner and/or injector apparatuses are directed towards the cold spots.
The cold spots are typically formed in areas further away from the furnace arc as scrap located in these areas receives electrical energy at a reduced rate per ton of scrap. One example of a cold spot is the region in line with a bisection of the angle between the electrodes where current density is relatively lower. Another example of a cold spot is the sump area which includes the tapping spout, due to its location away from the arc. Still another cold spot occurs at the slag door due to excessive heat losses to ambient air which infiltrates through this area. An even further common source for cold spots in furnaces occurs at the places where additional materials are injected, such as slag forming material, direct reduced iron, lime, etc., (which is inserted through a slag door or through an opening in the furnace side wall) due to the heat consumption of these materials as they melt down.
Prior art solutions to these challenges have been to incorporate additional burners and/or injectors around the furnace that target the cold spots. Electric arc furnaces equipped with burners and/or injectors located at cold spots have improved uniformity of scrap melting and have reduced build-ups of materials at the cold spots. Their location is chosen to avoid further overheating of hot spots that result from the rapid melting of scrap located between the electrode and the furnace shell. More specifically, the burners and/or injectors are located as far away from hot spots as is practically possible and the burner flame outlet opening direction is chosen so that flame penetration occurs predominantly into the scrap pile located at the cold spots and not to already heated portions of the furnace.
The burners and/or injectors are typically radially distributed around the furnace. Because the sump area is flooded with molten metal during tapping, burners and/or injectors are not installed in the sidewalls. Rather, these sump burners and/or injectors are inserted through and mounted to a balcony panel which forms a ceiling over the sump area. The balcony panel is rigidly attached to the sidewalls and may be distinguished from the EAF roof which is retractable from the sidewalls.
Burners and/or injectors are subjected to harsh conditions in EAFs, including intense radiative heat, convective heat transfer from hot furnace gases, slagging caused by splashing slag, and blowback of injected oxygen. In order to prolong the useful life of such burners and/or injectors, they are often mounted in panels that at least partially shield them from such harsh conditions. The panels are sometimes water-cooled.
Collectively, a burner, lance, burner/lance, injector, burner/lance/injector, or burner/injector mounted in such a panel may be referred to as burner and/or injector panel apparatus.
Typically, oxygen injection for the decarburization must wait until the melting phase of the process is substantially complete before starting high velocity injection of oxygen. This is since the burners cannot effectively deliver high velocity oxygen before then because some portions of unmelted charge may exist between the burners/lances and the liquid metal or metal melt. The oxygen flow would be deflected, potentially causing severe damage to the furnace and burner/injector panel.
This fact is further aggravated by the generally spherical shape of most EAF furnace structures. Melting of the metal typically occurs in the middle, lower portion of the melt and expands to fill the sides. Early in the melting phase a high velocity oxygen stream has less effect and/or ability to penetrate a not fully melted charge (metal) to decarburize the metal melt.
The same philosophy that is used in selecting the location of additional burner panel apparatuses is used to select the location of other injector apparatuses or burner/injectors for use in decarburization. When located adjacent the cold spots, the exothermic energy of melt refining can be used more effectively to melt the scrap without overheating the hot spots.
The discharge velocity of the oxygen stream from the burner and/or injector apparatus is to be chosen to allow the injected jet of oxygen to penetrate the slag and to react with the iron-carbon melt without excessive molten metal splashing on the furnace walls and electrode(s). However, inadvertent metal splashing does occur and is a common cause of apparatus failure. Those skilled in the art understand that the angle formed by the jet of oxygen and the horizontal slag surface (termed angle of attack) must not be too small or the injected jet of oxygen may not penetrate into the slag deeply enough. They further understand that the angle of attack must not be too great or blow back may occur with damage to the burner and/or injector apparatus.
Combined injection of carbon and oxygen via various apparatus, including dedicated lances in and around the furnace wall has become a common practice for adding extra heat to the process. Typically, the supply of carbon flow for injection is obtained from a carbonaceous material dispenser, such as a compressed gaseous carrier comprising compressed air, natural gas, nitrogen, and/or the like.
The use of the burners together with carbon and oxygen lances has allowed electric steelmakers to substantially reduce electrical energy consumption and to increase furnace production rate due to the additional heat input generated by the oxidation of carbon, and by significant increases in electric arc thermal efficiency achieved by the formation of a foamy slag layer that insulates the electric arc from heat losses. The foamy slag also stabilizes the electric arc and therefore allows for a higher electrical power input rate. The foamy slag layer is created by CO bubbles which are formed by the oxidation of injected carbon to CO. The increased flow of injected carbon creates increased localized CO generation. Accordingly, most EAF furnace units also comprise a post production means for removing or reducing CO levels in the off gas such as post-combustion burners. Mixing of the CO with oxygen inside of the electric arc furnace is desirable but very difficult to arrange without excessive oxidation of the slag and electrodes. Accordingly, the art field has developed postproduction means for treating the high CO content of the off gas.
Most modern electric arc furnaces are equipped with all or some of the above-mentioned means for auxiliary thermal and/or chemical energy input. Along with improvements in the design and operation of metal melting furnaces have come improvements in panel design. For example, various burner panel configurations are disclosed in U.S. Pat. No. 4,703,336; U.S. Pat. No. 5,444,733; U.S. Pat. No. 6,212,218; U.S. Pat. No. 6,372,010; U.S. Pat. No. 5,166,950; U.S. Pat. No. 5,471,495; U.S. Pat. No. 6,289,035; U.S. Pat. No. 6,614,831; U.S. Pat. No. 5,373,530; U.S. Pat. No. 5,802,097; U.S. Pat. No. 6,999,495; and U.S. Pat. No. 6,342,086. Such prior art patents have proven to be beneficial. For example, U.S. Pat. No. 6,999,495 has found wide applicability for increasing spatial energy coverage in a furnace. Likewise, U.S. Pat. No. 6,614,831 has found applicability in extending the reach of various tools, such as a burner or a lance, into the interior of a furnace.
Because sump burner and/or injector panel apparatuses are installed outside of the furnace area enclosed by the hearth, they are located a relatively greater distance from the surface of the molten metal and cold spots. Because the flame, oxygen jet, or particle stream must reach farther before it reaches the molten metal or cold spot, the jet becomes relatively less coherent in comparison to jets which are injected from relatively closer locations. Thus, the flame, oxidant, or particles are no longer directed to a relatively small area and the effectiveness of the jet is very limited. Thus, there is a need for improved sump burner and/or injector apparatuses and methods and furnaces using the same that do not suffer from as much loss of jet coherence.
Many configurations currently exist for burner and/or injector panel apparatuses. For sump burner and/or injector panel apparatuses, they are typically mounted and located outside the hearth area on the top of the sump in the balcony panel. These sump burner and/or injector panel apparatuses have a fixed position. Thus, the direction of the flame, or injection of the oxidant or particles is fixed and may not be easily changed. More specifically, the angular orientation of the apparatus in each of the x, y, and z axes is fixed. If the direct causes the flame, oxidant or particles to be oriented or injected outside of the target area of the bath, the furnace must be shut down and the burner and/or injector panel apparatus uninstalled from the balcony panel. This requires careful removal or refractory plastic and a significant amount of furnace downtime. It must then be reinstalled in an orientation that achieves the desired flame or injection direction. If the opening in the balcony panel is not large enough to allow the burner and/or injector panel apparatus to be reinstalled with the correct orientation, the opening in the balcony panel must be modified. This requires greater capital investment and a lengthier furnace downtime. Thus, there is a need to provide sump burner and/or injector panel apparatuses that avoid these problems.
Various techniques have been designed for cooling panels that are used in EAFs. One type of cooling means is an empty cavity, the inside of which is sprayed with cooling water. Another type of cooling means is a serpentine conduit of cooling water that traverses from left to right and back along a plane that is typically oriented at a right angle to the slag layer. While these often achieve a fully satisfactory cooling effect, such bulky devices result in an overly large, heavy, and expensive panel body. Thus, there is a need for an improved sump burner and/or injector panel apparatuses that avoid these problems.